Heat transfer tube for heat pump application

ABSTRACT

A heat transfer tube and a heat exchanger incorporating at least one heat transfer tubes are provided. The heat transfer tube and the heat exchanger are configured to operate in both a heating mode and a cooling mode (e.g., to optimize the reversible function a heat pump). The heat transfer tube includes a tube body with an interior surface and an exterior surface. The tube body defining an outer diameter (Do) and a wall thickness (WT), wherein a ratio (WT/Do) the wall thickness (WT) to the outer diameter (Do) is between 0.061 and 0.071. The heat transfer tube includes a plurality of adjacent helical fins protruding circumferentially around the interior surface of the tube body, and at least one groove disposed between the plurality of adjacent helical fins. The configuration of the heat transfer tube(s) is optimal for the reversible function of the heat pump.

CROSS REFERENCE TO A RELATED APPLICATION

The application claims the benefit of U.S. Provisional Application No. 63/198,577 filed Oct. 28, 2020, the contents of which are hereby incorporated in their entirety.

BACKGROUND

The invention relates generally to heat transfer tubes for use in heat exchangers. In particular, the invention relates to a heat transfer tube that is configured to optimize its use within a heat exchanger for a heat pump, which is capable of operating in a reversible manner (i.e., able to switch between a heating mode and a cooling mode).

A heat pump is a type of is a type of vapor compression system that is capable of reversing the flow of refrigerant. Vapor compression systems (e.g., heat pumps) commonly include a compressor to both move and increase the pressure of the refrigerant, two heat exchangers (one indoor heat exchanger and one outdoor heat exchanger) to transfer heat to or from the refrigerant, and at least one expansion valve for regulating the flow of refrigerant. To make it possible for the heat pump to change the direction the refrigerant flows, heat pumps also commonly include a reversing valve. In a basic heat pump, the compressor compresses the refrigerant and delivers it downstream through the reversing valve, which delivers the refrigerant to the outdoor heat exchanger if the heat pump is operating in a cooling mode, or to the indoor heat exchanger if the heat pump is operating in a heating mode. When operating in a cooling mode, the refrigerant is passed from the outdoor heat exchanger through the expansion valve to the indoor heat exchanger. When operating in a heating mode, the refrigerant is passed from the indoor heat exchanger through the expansion valve to the outdoor heat exchanger. Regardless of whether in a heating mode or a cooling mode, the refrigerant is routed back through the reversing valve back into the compressor, completing the cycle.

In recent years, there has been a focus on improving the heat exchangers (both the indoor heat exchanger and the outdoor heat exchanger) to increase the efficiency of the heat pumps. Commonly, heat exchangers incorporate one or more tubes to circulate refrigerant and transfer heat to or from an air supply (e.g., for a residential home, etc.). This heat is transferred through the tube walls via conduction. Many heat exchangers also utilize fins in thermally conductive contact with the outside of the tubes to provide increased surface area across which heat can be transferred. To improve the ability of the heat exchanger tubes to transfer heat through the tube walls, the tubes are often internally enhanced. These internally enhanced tubes are typically fabricated via an extrusion or drawings process and mechanically expanded into the fins to assure good metal-to-metal contact between the tubes and the fins. Often times copper, or alloys thereof, are used due to copper's mechanical properties, which enable helically shaped enhancement profiles to be fabricated with the extrusion process. However, in recent years, the industry has started to move from copper to aluminum, primary due to the fluctuating, often high, price of copper relative to aluminum. Aluminum, and alloys thereof, have inherently different mechanical properties that historically have limited its ability to be manufactured. In addition, due to the properties of the aluminum, historically, aluminum heat transfer tubes have a thicker tube wall (relative to tubes made of copper), which causes a smaller internal diameter, resulting in an increased pressure drop. As such, selecting an optimal configuration, that is capable of being manufactured, for an aluminum heat transfer tube often requires a balance between heat transfer improvement and pressure drop penalty. Although there are many different configurations of aluminum heat transfer tubes, new aluminum heat transfer tube configurations are always welcome.

Accordingly, there remains an ongoing need for new aluminum heat transfer tube configurations that are more efficient and capable of being more easily manufactured.

BRIEF DESCRIPTION

According to one embodiment, a heat transfer tube for operating in both a heating mode and a cooling mode is provided. The heat transfer tube includes a tube body defining an interior surface and an exterior surface, and a plurality of adjacent helical fins disposed around the interior surface of the tube body. The tube body defining an outer diameter (D_(o)) and a wall thickness (W_(T)), wherein a ratio (W_(T)/D_(o)) of the wall thickness (W_(T)) to the outer diameter (D_(o)) is between 0.061 and 0.071. The heat transfer tube includes at least one groove disposed between the plurality of adjacent helical fins. Each respective groove defines a groove width. Each respective helical fin defines a fin height, a fin tip width, a fin base width, a fin apex angle, and a fin helix angle. The interior surface of the tube body further includes a non-fin weld area, the non-fin weld area defining a non-fin height and a non-fin width.

In accordance with additional or alternative embodiments, the heat transfer tube provides a Cavallini factor between 1.67 and 2.22.

In accordance with additional or alternative embodiments, the tube body is made of at least one of: an aluminum and an aluminum alloy.

In accordance with additional or alternative embodiments, a cross-section of the heat transfer tube defines between 41 and 48 helical fins.

In accordance with additional or alternative embodiments, the outside diameter is between 6.85 mm and 7.14 mm.

In accordance with additional or alternative embodiments, the wall thickness is between 0.410 mm and 0.510 mm.

In accordance with additional or alternative embodiments, the fin height is between 0.144 mm and 0.248 mm.

In accordance with additional or alternative embodiments, the fin tip width is between 0.096 mm and 0.156 mm.

In accordance with additional or alternative embodiments, the fin base width is between 0.18 mm and 0.24 mm.

In accordance with additional or alternative embodiments, the fin apex angle is between 19° and 35°.

In accordance with additional or alternative embodiments, the fin helix angle is between 13° and 23°.

In accordance with additional or alternative embodiments, the groove width is between 0.102 mm and 0.221 mm.

According to another aspect of the disclosure, a heat exchanger for operating in both a heating mode and a cooling mode is provided. The heat exchanger includes a plurality of fins and at least one heat transfer tube configured to pass a fluid therethrough. The at least one heat transfer tube extending through the plurality of fins. Each respective heat transfer tube include a tube body defining an interior surface and an exterior surface, and a plurality of adjacent helical fins disposed around the interior surface of the tube body. The tube body defining an outer diameter (D_(o)) and a wall thickness (W_(T)), wherein a ratio (W_(T)/D_(o)) of the wall thickness (W_(T)) to the outer diameter (D_(o)) is between 0.061 and 0.071. The heat transfer tube includes at least one groove disposed between the plurality of adjacent helical fins. Each respective groove defines a groove width. Each respective helical fin defines a fin height, a fin tip width, a fin base width, a fin apex angle, and a fin helix angle. The interior surface of the tube body further includes a non-fin weld area, the non-fin weld area defining a non-fin height and a non-fin width.

In accordance with additional or alternative embodiments, the heat transfer tube provides a Cavallini factor between 1.67 and 2.22.

In accordance with additional or alternative embodiments, the tube body is made of at least one of: an aluminum and an aluminum alloy.

In accordance with additional or alternative embodiments, a cross-section of the heat transfer tube defines between 41 and 48 helical fins.

In accordance with additional or alternative embodiments, the outside diameter is between 6.85 mm and 7.14 mm, and the wall thickness is between 0.410 mm and 0.510 mm.

In accordance with additional or alternative embodiments, the fin height is between 0.144 mm and 0.248 mm, the fin tip width is between 0.096 mm and 0.156 mm, and the fin base width is between 0.18 mm and 0.24 mm.

In accordance with additional or alternative embodiments, the fin apex angle is between 19° and 35°, and the fin helix angle is between 13° and 23°.

In accordance with additional or alternative embodiments, the groove width is between 0.102 mm and 0.221 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the disclosure, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The following descriptions of the drawings should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike:

FIG. 1 is a perspective view of an exemplary heat exchanger incorporating an exemplary heat exchanger tube, in accordance with one aspect of the disclosure.

FIG. 2 is a perspective side view of the exemplary heat exchanger tube of FIG. 1, in accordance with one aspect of the disclosure.

FIG. 3 is a cross-sectional side view of the exemplary heat exchanger tube of FIGS. 1 and 2 illustrating a plurality adjacent helical fins protruding circumferentially around the interior surface of the tube body, in accordance with one aspect of the disclosure.

FIG. 4 is a cross-sectional front view of a portion of the exemplary heat exchanger tube of FIGS. 1-3 illustrating the plurality of adjacent helical fins from a closer perspective, in accordance with one aspect of the disclosure.

FIG. 5 is a cross sectional front view of a portion of the exemplary heat exchanger tube of FIGS. 1-3 illustrating a non-fin weld area disposed on the interior surface of the tube body, in accordance with one aspect of the disclosure.

DETAILED DESCRIPTION

As will be described below, a heat transfer tube with improved efficiency and manufacturability, and a heat exchanger incorporating the same are provided. Specifically, the features of the heat transfer tube described herein may enable a more efficient operation for a heat pump, which is capable of operating in both a heating mode and a cooling mode. The heat transfer tube described herein has an optimal configuration that balances the heat transfer improvement (in both condensation and evaporation) with the associated pressure drop penalty. It was found that the configuration of the different features of the heat transfer tube described herein results in a surprisingly high performance when compared to other designs currently used in the industry. It will be appreciated that this surprisingly high performance is directly tied to the use of the heat transfer tube within a heat pump, which is capable of reversing the flow of refrigerant to switch between a cooling mode and a heating mode. For example, the heat transfer tube described herein may not be optimized for use within a system that is only capable of providing cooling. It will be appreciated that the heat transfer tube described herein may be made of aluminum (or alloy thereof), and may only be manufactured using a welded-rolled formed process (e.g., compared to an extrusion process commonly used to manufacture heat transfer tubes made of copper or copper alloys) in certain instances. The manufacturing process of the heat transfer tube is described in further detail below. It is envisioned that by manufacturing the heat transfer tube out of aluminum (or aluminum alloy), instead of copper, that the associated costs of manufacturing the heat transfer tube may be more predictable and relatively lower (when compared to heat transfer tubes made of copper or copper alloys).

With reference now to the Figures, a perspective view of an exemplary heat exchanger 200 incorporating an exemplary heat exchanger tube 100 is shown in FIG. 1. As shown, the heat exchanger 200 may be a round tube plate fin (RTPF) type heat exchanger, including a plurality of fins 210 and at least one heat transfer tube 100. For purposes of clarity, although the heat exchanger 200 is shown to include only one heat transfer tube 100, which is shown to include an inlet line 130 at one end, an outlet line 140 connected at another end, and a bend 150 therebetween, it will be evident to a person of ordinary skill in the art, that more heat transfer tubes 100 may be added to the heat exchanger 200. It should be appreciated that the heat transfer tube 100 may be separated in multiple sections (e.g., where the bend 150 portion is connected to the inlet line 130 and the outlet line 140) in certain instances, or formed as a single tube unitary tube in other instances.

As mentioned above, the heat transfer tube(s) 100 may be made of an aluminum or an aluminum alloy in certain instances. For example, the heat transfer tube(s) 100 may be made from aluminum alloys selected from 1000 series, 3000 series, 5000 series, or 600 series aluminum alloys in certain instances. Likewise, the fins 210 too may be made of an aluminum or an aluminum alloy in certain instances. For example, the fins 210 may be made from aluminum alloys selected from the 1000 series, 3000 series, 6000 series, 7000 series, or 8000 series aluminum alloys in certain instances. It will be appreciated that the fins 210 and/or the heat transfer tube(s) 100 may be made from other aluminum alloys in certain instances. Regardless of the type of material(s) used to manufacture the fins 210 and/or the heat transfer tube(s) 100, the fins 210 may be configured as plate-like elements spaced along the length of the heat transfer tube(s) 100 (e.g., using an interference fit in certain instances). As shown in FIG. 1, the fins 210 may be provided between a pair of end plates or tube sheets 220, 230. It is envisioned that the fins 210 may help to increase the surface area for which heat may be transferred between the refrigerant (circulating through the heat transfer tube(s) 100) and the air passing over the heat exchanger 200. As mentioned above, the heat transfer tube(s) 100 may be specifically designed to increase the efficiency of a heat pump, which is capable of switching (e.g., by reversing the flow of refrigerant) between a heating mode and a cooling mode. It will be evident to a person of ordinary skill in the art, that the heat transfer tube(s) 100 may not be optimal for use within a system that is only capable of operating in a cooling mode.

It will be appreciated that the increase in efficiency of the heat pump caused by the heat transfer tube(s) is attributable to the configuration of the different features of the heat transfer tube(s) 100. An exemplary heat transfer tube 100 is shown in FIGS. 2 and 3. FIG. 2 is provided to illustrate the heat transfer tube 100 without the plurality of fins 200 (as shown in FIG. 1). FIG. 3 is provided to illustrate the interior surface 121 and the exterior surface 122 of the tube body 120. As shown in FIG. 3, the tube body 120 may define an outer diameter D_(o) and a wall thickness W_(T). It was found that by controlling the ratio (W_(T)/D_(o)) of the wall thickness W_(T) to the outer diameter D_(o) that the heat transfer tube 100 may be optimized for use within a heat pump. In certain instances the ratio (W_(T)/D_(o)) of the wall thickness W_(T) to the outer diameter D_(o) is between 0.061 and 0.071.

As shown in FIG. 3, the heat transfer tube 100 includes a plurality of adjacent helical fins 110 (shown in FIG. 4) protruding circumferentially around the interior surface of the tube body 120. As shown in FIG. 4, at least one groove 160 (viewed as the void or space between adjacent fins 110) may be disposed between the plurality of adjacent helical fins 110. Each respective groove may be viewed to have a defined groove width W_(G). Each respective helical fin 110 may be viewed to have a defined fin height H_(F), fin tip width W_(FT), fin base width W_(FB), fin apex angle Θ_(FA), and fin helix angle Θ_(HA) (shown in FIG. 3). In addition, the interior surface 121 of the tube body 120 may also include a non-fin weld area 170 (shown in FIG. 5). It should be appreciated that this non-fin weld area 170 may be a result of the welded-rolled formed manufacturing process used to produce the heat transfer tube 100 described herein. As shown in FIG. 5, the non-fin weld area 170 may be viewed to have a defined non-fin height H_(NF) and non-fin width W_(NF).

As mentioned above, the heat transfer tube 100 described herein may be manufactured using a welded rolled formed manufacturing process. This process may include starting with a rectangular sheet of aluminum (or alloy thereof) that is manufactured to include fins 110. This rectangular sheet of aluminum (or alloy thereof) is rolled using a rolling machine into a tubular shape. These rolling machines may utilize a high-frequency electrical current to forge the seam or joint of the heat transfer tube 100. It should be appreciated that other methods may be used to forge the seam or joint of the heat transfer tube 100 (e.g., tig-type, mig-type, or any suitable electrical-type welding, etc. may be used in certain instances). The non-fin weld area 170 described above may be viewed as this seam or joint of the heat transfer tube 100. Although described as a non-fin weld area 170, it will be appreciated that partial or irregular fins 110 may be present within the non-fin weld area 170. These partial or irregular fins 110 may be caused as a result of the welding process, which may consume or distort the fins 110 from their original form (i.e. how they existed on the rectangular sheet of aluminum). It should be appreciated that the dimensions of the non-fin weld area 170 may be directly associated with the limitations of the welded rolled formed manufacturing process. For example, although it may be ideal to minimize the non-fin height H_(NF) and/or the non-fin width W_(NF) in order to maximize the number of helical fins 110 and/or internal surface area within the heat transfer tube 100, the welded rolled formed manufacturing process inherently requires at least a certain sized non-fin weld area 170. In certain instances the non-fin width W_(NF) should be less than 1.4 mm. It should be appreciated that the non-fin weld area 170 should be ignored with respect to average fin and average wall thickness W_(T) in certain instances. It will be evident to a person of ordinary skill in the art that the non-fin weld area 170 is created a result of a welded rolled formed manufacturing process and not created by any irregularities from an extrusion-type manufacturing process.

As mentioned above, the heat transfer tube 100 described herein is optimized for use within a heat pump, which is capable of reversing the flow of refrigerant to switch between a heating mode and a cooling mode. It was found when optimizing the heat transfer tube 100 for use within a heat pump the heat transfer tube 100 provides a Cavallini factor between 1.67 and 2.22 in certain instances. The Cavallini factor may be expressed in terms of the following formula: [[2*(number of fins)*(height of the fins)*(1−Sin(Θ_(FA)/2))/((3.14)(internal diameter of the heat transfer tube)*Cos(Θ_(FA)/2))+1]/Cos Θ_(HA)]{circumflex over ( )}2. To produce such a heat transfer tube 100 with such a Cavallini factor, the tube body 120 and the helical fins 110 should be precisely configured. For example, the cross-section of the heat transfer tube 100 should define between 41 and 48 helical fins 110 (i.e., when viewed from the front of the heat transfer tube 100). It will be appreciated that the heat transfer tube 100 described herein may have 48 helical fins 110 in certain instances.

It is envisioned that the heat transfer tube 100 described herein may be configured to minimize its outside diameter D_(o) (shown in FIG. 3), while maximizing its internal diameter (i.e. D_(o)−W_(T)), which may help minimize the pressure drop generated by the heat transfer tube 100. The outside diameter D_(o) is between 6.85 mm and 7.14 mm and the wall thickness W_(T) (shown in FIG. 4) is between 0.410 mm and 0.510 mm in certain instances. It will be appreciated that the outside diameter D_(o) is less than 7.10 mm (e.g., 7.05 mm) and the wall thickness W_(T) is less than 0.50 mm (e.g., 0.46 mm) in certain instances, which may help minimize the pressure drop generated by the heat transfer tube 100. To effectively function within the heat pump, the heat transfer tube 100 should not only be configured to minimize pressure drop, but should also be configured to maximize its heat transfer capabilities. As shown above by the formula for the Cavallini factor, the Cavallini factor (which is illustrative of the heat transfer capabilities of the heat transfer tube 100) is dependent, at least in part, on the configuration of the helical fins 110.

As shown in FIG. 4, each respective helical fin 110 may be viewed to have a defined fin height H_(F), fin tip width W_(FT), fin base width W_(FB), fin apex angle Θ_(FA), and fin helix angle Θ_(HA) (shown in FIG. 3). The fin height H_(F) is between 0.144 mm and 0.248 mm (e.g., 0.23 mm) in certain instances. The fin tip width W_(FT) is between 0.096 mm and 0.156 mm (e.g., 0.11 mm) in certain instances. The fin base width W_(FB) is between 0.18 mm and 0.24 mm (e.g., 0.21 mm) in certain instances. The fin apex angle Θ_(FA) is between 19° and 35° (e.g., 25°) in certain instances. The fin helix angle Θ_(HA) is between 13° and 23° (e.g., 18°) in certain instances. As shown in FIG. 4, the groove(s) 160, disposed between the helical fins 110, may be viewed to have a defined groove width W_(G). The groove width W_(G) is between 0.102 mm and 0.221 mm (e.g., 0.19 mm) in certain instances. It will be evident to a person of ordinary skill in the art that these dimensions are given in respect to the heat transfer tube 100 prior to joining with the plurality of fins 210, which may be joined using pressure expansion or mechanical expansion (either of which may cause deformation of one or more of the dimensions). It should be appreciated that the configuration of the fins 110 and the grooves 160, as described above, were selected so as to optimize the function of the heat transfer tube 100 within a heat pump, which, as mentioned above, is capable of reversing the flow of refrigerant so as to switch between a heating mode and a cooling mode. As such, the heat transfer tube 100 describe herein may not be optimized for use within a system that is only capable of providing cooling, such as an air conditioner.

The use of the terms “a” and “and” and “the” and similar referents, in the context of describing the invention, are to be construed to cover both the singular and the plural, unless otherwise indicated herein or cleared contradicted by context. The use of any and all example, or exemplary language (e.g., “such as”, “e.g.”, “for example”, etc.) provided herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed elements as essential to the practice of the invention.

While the present disclosure has been described with reference to an exemplary embodiment or embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from the essential scope thereof. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this present disclosure, but that the present disclosure will include all embodiments falling within the scope of the claims. 

What is claimed is:
 1. A heat transfer tube for operating in both a heating mode and a cooling mode, the heat transfer tube comprising: a tube body comprising an interior surface and an exterior surface, the tube body defining an outer diameter (D_(o)) and a wall thickness (W_(T)), wherein a ratio (W_(T)/D_(o)) of the wall thickness (W_(T)) to the outer diameter (D_(o)) is between 0.061 and 0.071; and a plurality of adjacent helical fins protruding circumferentially around the interior surface of the tube body, at least one groove disposed between the plurality of adjacent helical fins, each respective groove defining a groove width, each respective helical fin defining a fin height, a fin tip width, a fin base width, a fin apex angle, and a fin helix angle, wherein the interior surface of the tube body further comprises a non-fin weld area, the non-fin weld area defining a non-fin height and a non-fin width.
 2. The heat transfer tube of claim 1, wherein the heat transfer tube provides a Cavallini factor between 1.67 and 2.22.
 3. The heat transfer tube of claim 1, wherein the tube body is comprised of at least one of: an aluminum and an aluminum alloy.
 4. The heat transfer tube of claim 1, wherein a cross-section of the heat transfer tube defines between 41 and 48 helical fins.
 5. The heat transfer tube of claim 1, wherein the outside diameter is between 6.85 mm and 7.14 mm.
 6. The heat transfer tube of claim 1, wherein the wall thickness is between 0.410 mm and 0.510 mm.
 7. The heat transfer tube of claim 1, wherein the fin height is between 0.144 mm and 0.248 mm.
 8. The heat transfer tube of claim 1, wherein the fin tip width is between 0.096 mm and 0.156 mm.
 9. The heat transfer tube of claim 1, wherein the fin base width is between 0.18 mm and 0.24 mm.
 10. The heat transfer tube of claim 1, wherein the fin apex angle is between 19° and 35°.
 11. The heat transfer tube of claim 1, wherein the fin helix angle is between 13° and 23°.
 12. The heat transfer tube of claim 1, wherein the groove width is between 0.102 mm and 0.221 mm.
 13. A heat exchanger for operating in both a heating mode and a cooling mode, the heat exchanger comprising: a plurality of fins; and at least one heat transfer tube configured to pass a fluid therethrough, the at least one heat transfer tube extending through the plurality of fins, each respective heat transfer tube comprising: a tube body comprising an interior surface and an exterior surface, the tube body defining an outer diameter (D_(o)) and a wall thickness (W_(T)), wherein a ratio (W_(T)/D_(o)) the wall thickness (W_(T)) to the outer diameter (D_(o)) is between 0.061 and 0.071; and a plurality of adjacent helical fins protruding circumferentially around the interior surface of the tube body, at least one groove disposed between the plurality of adjacent helical fins, each respective groove defining a groove width, each respective helical fin defining a fin height, a fin tip width, a fin base width, a fin apex angle, and a fin helix angle, wherein the interior surface of the tube body further comprises a non-fin weld area, the non-fin weld area defining a non-fin height and a non-fin width.
 14. The heat exchanger of claim 13, wherein the heat transfer tube provides a Cavallini factor between 1.67 and 2.22.
 15. The heat exchanger of claim 13, wherein the tube body is comprised of at least one of: an aluminum and an aluminum alloy.
 16. The heat exchanger of claim 13, wherein a cross-section of the heat transfer tube defines between 41 and 48 helical fins.
 17. The heat exchanger of claim 13, wherein the outside diameter is between 6.85 mm and 7.14 mm, and the wall thickness is between 0.410 mm and 0.510 mm.
 18. The heat exchanger of claim 13, wherein the fin height is between 0.144 mm and 0.248 mm, the fin tip width is between 0.096 mm and 0.156 mm, and the fin base width is between 0.18 mm and 0.24 mm.
 19. The heat exchanger of claim 13, wherein the fin apex angle is between 19° and 35°, and the fin helix angle is between 13° and 23°.
 20. The heat exchanger of claim 13, wherein the groove width is between 0.102 mm and 0.221 mm. 